The present invention pertains to the field of analyte detection and, more specifically, to an automated system and method for the use of fluorimetric and colorimetric detection inks and capillary action to detect one or more target analytes, including explosives, narcotics, organophosphates, gunshot residue and toxic industrial chemicals.
The detection of small amounts of explosives is important for the prevention of terrorist attacks and for the safeguarding of civilians, military personnel and bases, airports and other transportation locations, and tourist and commercial venues. The low volatility of many explosives, such as TNT, RDX, and PETN, makes vapor sampling difficult and largely inefficient, especially at low temperatures. Thus, efficient solid-state sampling techniques are desirable for many applications. Chemical sensors are often desired because they are able to detect trace amounts of explosives and can be packaged into simple-to-use, low-cost devices. Conventional detection methods, such as X-ray diffraction, nuclear quadrupole resonance, and gas chromatography-mass spectrometry, though highly sensitive, are expensive, difficult to maintain, susceptible to false-positives, and are not easily manufactured into low power, portable devices. Low end systems, while physically simple compared to the high end systems, require more complex user interaction and interpretation.
A major source of terrorist funding is gained through narcotics trafficking. This relationship implies that there could be a correlation between narcotics and terrorist weapons, including explosives. Therefore, the ability to detect narcotics concurrently with explosives may potentially be valuable in fighting the terrorist network at large. In addition to the international needs, narcotics detection is also a focus for other domestic criminal and forensic applications. Narcotics of particular interest are heroin, cocaine, marijuana, and methamphetamines. Analytical instrumentation, such as FT-IR, Raman, GC-MS, and IMS, may be used to identify specific drugs, but these are typically ill-suited for widespread field use because of their size and/or expense. Existing colorimetric detection technology employed in presumptive forensic field-test kits is used to detect visible quantities of narcotics that are typically low milligram quantities. Many of these kits require sampling and dispensing an amount of one or more solutions into a reservoir, visually interpreting a color change, and referencing a color chart to look for a specific color while discounting other colors. This process can be time consuming, subject to bias in an individual's perception of color. The overall performance is subject to change based on an individual's eye sight and external lighting conditions. Automating the detection of these colorimetric kits would at least remove the subjectivity in detection and performance dependency on external lighting conditions.
Like narcotics, gunshot residue (GSR) is an important analyte of interest for both domestic and international operations. GSR is generated upon firing a weapon and is deposited on surfaces surrounding the weapon, including a hand of a shooter. GSR is produced from two sources: a primer and a propellant of the weapon's ammunition. The primer often contains heavy metal components, e.g., lead, barium and antimony, and the propellant usually contains nitrate-containing components, e.g., nitrocellulose. Criminal investigators can use GSR evidence in their work to determine many circumstances of a case, e.g., a firing distance and identity of the shooter. Identifying shooters is often done by collecting residue from the hand, either by dabbing the hand with adhesive stubs (which is relatively more efficient) or swiping with dry or wetting fabric/paper (which is relatively less efficient). The amount of residue deposited on the hand is small and dissipates over time and with activity, e.g., hand washing or wiping.
Currently, GSR can be detected in colorimetric presumptive tests or through a laboratory analysis. The presumptive tests usually focus on detection of propellant residue since there is more of it, and, therefore, the colorimetric signal is easier to observe visually. However, these tests are fraught with false positives, as nitrate-containing compounds are often found in the environment, e.g., fertilizers, food products, etc. Colorimetric tests for lead can also be used as presumptive tests, although the lead particles are so small that, oftentimes, the color produced is not visible to the naked eye. Analytical tests usually focus on primer residue and can determine the presence of the metal particles. Destructive tests such as atomic absorption simply identify the presence of metals. Scanning electron microscopy (SEM) is the current gold standard in GSR detection because SEM can identify particles that are characteristic of GSR rather than simply identifying the presence of metals, which could be from other environmental sources, e.g., lead paint. Such characteristic particles contain all three of the main primer metals, i.e., lead, barium and antimony. Particle shape is also relevant to identifying the particles as being produced during the firing of a weapon. SEM can detect particles less than a micron in size and so has the advantage of detecting particles far smaller than those visible to the naked eye. However, SEM has the disadvantage of being expensive and time-consuming, with results often not being available to law enforcement for weeks or months.
A field presumptive test is of great value to law enforcement as it provides immediate, actionable intelligence for investigators. However, a confirmatory test is often needed to rule out environmental false positives and assist in any legal action against a suspect. Since the amount of GSR on a shooter's hand is small, efficient sample collection is vital. Running a field presumptive test can be problematic if the test is destructive (i.e., the GSR is consumed in the test and no longer available for a confirmatory test), as is often the case, especially with a nitrate-based test, which uses strong acids (e.g., >70% sulfuric acid, which destroys the characteristic GSR particles). Therefore, it would be advantageous to be able to collect a single sample that could be processed both in the field for a field presumptive test and subsequently in a confirmatory test.
A multi-assay tool capable of detecting explosives, narcotics, and GSR in a single instrument and correlating this data would be a valuable tool in combating terrorist and criminal activities, both domestically and internationally. Optimization of such a tool for widespread use would require simplicity of use, portability, low power and maintenance requirements to be incorporated in a low cost device. Additional advantages would be gained by minimizing user interactions, particularly the number of analysis steps and ambiguity in user interpretation. Importantly, such an automated tool would allow for greater sensitivity and eliminated dependency on external lighting conditions and viewer's eyesight.